WO2022054781A1

WO2022054781A1 - Method for producing lithium secondary battery, and lithium secondary battery

Info

Publication number: WO2022054781A1
Application number: PCT/JP2021/032784
Authority: WO
Inventors: 克行 ▲高▼橋; 祐輝酒井; 貴洋齊藤; 彰文菊池
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2020-09-08
Filing date: 2021-09-07
Publication date: 2022-03-17
Also published as: JPWO2022054781A1

Abstract

One embodiment of the present invention provides a method for producing a lithium secondary battery which is provided with a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the negative electrode contains lithium metal or a lithium alloy that serves as an active material in a charged state. This method for producing a lithium secondary battery comprises: a process for producing a positive electrode mixture paste that contains a positive electrode active material and an oxo acid of phosphorus; and a process for drying the positive electrode mixture paste. Another embodiment of the present invention provides a lithium secondary battery which is provided with: a positive electrode that comprises a positive electrode mixture containing a positive electrode active material; a negative electrode that contains lithium metal or a lithium alloy which serves as an active material in a charged state; and a nonaqueous electrolyte. With respect to this lithium secondary battery, a peak of P2p is present at 133 eV or less in the spectrum of the positive electrode mixture as determined by X-ray photoelectron spectroscopy.

Description

Manufacturing method of lithium secondary battery and lithium secondary battery

The present invention relates to a method for manufacturing a lithium secondary battery and a lithium secondary battery.

Lithium secondary batteries are widely used in personal computers, electronic devices such as communication terminals, automobiles, etc. due to their high energy density. A lithium secondary battery generally includes an electrode body having a pair of electrodes and a non-aqueous electrolyte interposed between the electrodes, and is configured to be charged and discharged by the movement of lithium ions between the electrodes.

In the lithium secondary batteries currently in practical use, it is common to use a negative electrode active material (carbon material, semi-metal material, metal oxide material, etc.) that occludes and releases lithium ions in the negative electrode. When such a negative electrode active material is used, there is a problem that the energy density becomes low.

As a means of increasing the energy density, the use of lithium metal for the negative electrode can be mentioned. Lithium metal has a high capacity per unit volume and unit mass, and has a low operating potential. Therefore, by utilizing the precipitation reaction and the elution reaction of the lithium metal as the charge / discharge reaction of the negative electrode, a lithium secondary battery having a high energy density can be obtained.

Patent Document 1 describes a lithium secondary battery comprising a negative electrode made of a lithium metal or a lithium alloy as an active material and a positive electrode made of a metal oxide, a metal sulfide, etc. as an active material via an organic electrolytic solution and a separator. , It is described that the organic electrolytic solution contains a phosphite diester. Then, in the Example, it is described that an electrolytic solution in which ethylene carbonate (EC), dimethyl carbonate (DME), and diethyl phosphite are mixed in a volume ratio of 60:39: 1 is used.

Patent Document 2 describes Li _1.18 Ni _0.10 Co _0.17 Mn _0.55 O ₂ , acetylene black, and PVDF 94: 4.5, which are positive electrode active substances, using N-methylpyrodrin as a dispersion medium. An example is described in which 1% by mass of phosphonic acid (H ₃ PO ₃ ) is added to a mixture mixed at a mass ratio of: 1.5 with respect to the mass of the positive electrode active material to obtain a positive electrode mixture paste. There is. Further, a non-aqueous electrolyte power storage element in which a positive electrode produced by using the positive electrode mixture paste and a negative electrode containing graphite as an active material are combined is described.

Japanese Patent Application Laid-Open No. 5-190205 JP-A-2018-125209

In a negative electrode using a negative electrode active material that occludes and discharges lithium ions, lithium ions are inserted into the negative electrode active material during charging, and lithium ions are released from the negative electrode active material during discharging. That is, the lithium metal precipitation reaction and elution reaction are not used as the charge / discharge reaction. Therefore, if such a negative electrode active material is used, the lithium metal does not grow like a dendrite during the precipitation reaction unless charging and discharging are performed under special conditions.
On the other hand, in the negative electrode using lithium metal, the precipitation reaction and elution reaction of lithium metal are used for charging and discharging. Therefore, when charging and discharging are repeated, the lithium metal grows like a dendrite during the precipitation reaction, causing a short circuit. There is. Therefore, in a lithium secondary battery that deposits lithium metal on the negative electrode by charging, a technique for suppressing a short circuit that occurs when charging and discharging are repeated is desired.

The present invention has been made based on the above circumstances, and an object thereof is to provide a lithium secondary battery capable of suppressing the occurrence of a short circuit, and a method for manufacturing the same.

The method for manufacturing a lithium secondary battery according to an embodiment of the present invention is a method for manufacturing a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the negative electrode is used as an active material in a charged state. The present invention comprises the preparation of a positive electrode mixture paste containing the above-mentioned lithium metal or lithium alloy, the positive electrode active material, and the oxo acid of phosphorus, and the drying of the above-mentioned positive electrode mixture paste.

The lithium secondary battery according to another embodiment of the present invention includes a positive electrode having a positive electrode mixture containing a positive electrode active material, a negative electrode containing a lithium metal or a lithium alloy as an active material in a charged state, and a non-aqueous electrolyte. A lithium secondary battery having a P2p peak of 133 eV or less in the spectrum of the positive electrode mixture obtained by X-ray photoelectron spectroscopy.

According to the method for manufacturing a lithium secondary battery of the present invention, it is possible to manufacture a lithium secondary battery in which the occurrence of a short circuit is suppressed. According to the lithium secondary battery of the present invention, the occurrence of a short circuit can be suppressed.

FIG. 1 is an external perspective view of a lithium secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of lithium secondary batteries according to an embodiment of the present invention.

First, the manufacturing method of the lithium secondary battery disclosed in the present specification and the outline of the lithium secondary battery will be described.

According to the manufacturing method, it is possible to manufacture a lithium secondary battery in which the occurrence of a short circuit is suppressed.

The present inventors say that in the process of manufacturing a lithium secondary battery including a negative electrode containing a lithium metal, by adding phosphorus oxo acid to the positive electrode mixture paste, a short circuit that occurs when charging and discharging are repeated can be suppressed. We have found that surprising events occur that cannot be predicted from the conventional wisdom of technology.

In carrying out the present invention, it is not necessary to clarify the reason why such an effect is obtained, but for example, the following can be considered.
Current concentration is one of the factors that cause the lithium metal to grow in a dendrite shape on the negative electrode by repeating charging. On the other hand, in the present invention, a positive electrode is prepared using a positive electrode mixture paste containing an oxo acid of phosphorus. By producing a positive electrode using such a positive electrode mixture paste, a film containing a phosphorus atom derived from phosphorus oxoacid is formed on the surface of the positive electrode active material. This coating is thought to suppress side reactions at the interface between the positive electrode active material and the non-aqueous electrolyte. When the side reaction is suppressed, the partial increase in resistance of the positive electrode is suppressed, and the current concentration is alleviated. As a result, it is considered that the dendrite-like growth of the lithium metal was inhibited in the negative electrode, and the occurrence of a short circuit could be suppressed.

The content of phosphorus oxoacid in the positive electrode mixture paste is preferably 0.05 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. By using such a positive electrode mixture paste, it is possible to further suppress the occurrence of a short circuit due to repeated charging and discharging.

The content of oxoacid of phosphorus in the positive electrode mixture paste is 0.1 parts by mass or more and 0.3 parts by mass or less with respect to 100 parts by mass of the positive electrode active material, and the positive electrode active material is Li [Li. It is preferable to contain a lithium transition metal composite oxide represented by the composition formula of _x Co _(1-x) ] O ₂ (0 ≦ x <0.5). In such a case, the capacity retention rate can be increased while suppressing the occurrence of a short circuit due to repeated charging and discharging.

According to the lithium secondary battery, the occurrence of a short circuit can be suppressed.

In carrying out the present invention, it is not necessary to clarify the reason why such an effect is obtained, but for example, the following can be considered.
For the lithium secondary battery, the peak of P2p present at 133 eV or less in the spectrum of the positive electrode mixture by X-ray photoelectron spectroscopy is that the compound present on the surface of the positive electrode mixture has a phosphorus atom in a specific chemical bond state. Is shown to include. It is presumed that the compound containing a phosphorus atom forms a film on the surface of the positive electrode active material. In the lithium secondary battery, such a coating suppresses a side reaction at the interface between the positive electrode active material and the non-aqueous electrolyte, thereby alleviating the current concentration. As a result, it is considered that the dendrite-like growth of the lithium metal was inhibited in the negative electrode, and the occurrence of a short circuit could be suppressed.

The sample used for the X-ray photoelectron spectroscopy (XPS) measurement of the positive electrode mixture is prepared by the following method. The lithium secondary battery is discharged with a current of 0.1 C to the discharge end voltage at the time of normal use, and is in a completely discharged state. Here, "during normal use" means a case where the lithium secondary battery is used by adopting the discharge conditions recommended or specified for the lithium secondary battery. The lithium secondary battery in a completely discharged state is disassembled, the positive electrode is taken out, the positive electrode is thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The dried positive electrode is cut out to a predetermined size (for example, 2 × 2 cm) and used as a sample for XPS measurement. The work from disassembling the lithium secondary battery to preparing the sample in XPS measurement is performed in an argon atmosphere with a dew point of −60 ° C. or lower, and the sample is enclosed in a transfer vessel and subjected to XPS measurement without exposure to the atmosphere. The equipment and measurement conditions used in the XPS measurement of the positive electrode mixture are as follows.
Equipment: "AXIS NOVA" from KRATOS ANALYTICAL
X-ray source: Monochromatic AlKα
Acceleration voltage: 15kV
Tube current: 10mA
Analytical area: 700 μm × 300 μm
Measurement range: P2p = 142 to 125 eV, C1s = 300 to 272 eV
Measurement interval: 0.1 eV
Measurement time: P2p = 72.3 seconds / time, C1s = 70.0 seconds / time Total number of times: P2p = 15 times, C1s = 8 times

The peak position of P2p in the above spectrum is a value obtained as follows. First, the peak of the binding energy attributed to sp2 carbon in C1s is set to 284.8 eV, and all the obtained spectra are corrected. Next, leveling processing is performed on each spectrum by removing the background using the linear method. In the spectrum after the leveling treatment, the binding energy showing the highest value in the range of 142 to 125 eV is defined as the peak position of P2p.

The positive electrode includes a positive electrode mixture layer containing the positive electrode mixture, and the volume density per unit area of the positive electrode mixture layer is preferably 3 mAh / cm ² or more. By using such a positive electrode, it is possible to increase the energy density of the lithium secondary battery while suppressing the occurrence of a short circuit due to repeated charging and discharging.

The capacity density per unit area of the positive electrode mixture layer shall be the value obtained by the following formula (a) when the design of the lithium secondary battery is clear, and the following capacity check when the design of the lithium secondary battery is unknown. The value shall be the value obtained by the test and the following formula (b). In the following formulas (a) and (b), "capacity density" refers to the volume density per unit area of the positive electrode mixture layer. Further, in the following formula (a), the "rated capacity" is completely charged after the lithium secondary battery is fully charged by adopting the charge / discharge conditions recommended or specified in the lithium secondary battery. Discharge capacity when discharged to the discharged state, and if a charger for the lithium secondary battery is prepared, discharge when discharged to the completely discharged state after charging by applying the charger. Refers to capacity. The "effective area" refers to the area where the positive electrode mixture layer and the negative electrode active material layer face each other.
(When the design of the lithium secondary battery is clear)
Rated capacity of lithium secondary battery (mAh) / Effective area of positive electrode mixture layer (cm ² ) = Capacity density (mAh / cm ² ) ... (a)
(If the design of the lithium secondary battery is unknown)
The capacity confirmation test of the positive electrode punched out to an arbitrary area by disassembling the lithium secondary battery is carried out. First, the lithium secondary battery is disassembled, the positive electrode is taken out, the non-aqueous electrolyte adhering to the taken out positive electrode is thoroughly washed with dimethyl carbonate, and the test battery is dried at room temperature for 24 hours and then with the lithium metal electrode as the counter electrode. To assemble. Pure metallic lithium is used for the lithium metal electrode here. A capacity confirmation test is carried out at a current value of 10 mA per 1 g of the positive electrode mixture layer. It is charged with a constant current until it reaches the end-of-charge voltage during normal use, and is fully charged. After pause, constant current discharge to the lower limit voltage during normal use. From the discharge capacity (mAh) obtained in the capacity confirmation test and the area of the positive electrode mixture layer (cm ² ) in the test battery, the capacity density per unit area of the positive electrode mixture layer (mAh /) is calculated by the following formula (b). Find cm ² ). The work from disassembling the lithium secondary battery to assembling the test battery is performed in an argon atmosphere with a dew point of -60 ° C or lower. In addition, "during normal use" is a case where the lithium secondary battery is used by adopting the charge / discharge conditions recommended or specified for the lithium secondary battery, and is used for the lithium secondary battery. When a charger is prepared, it means the case where the charger is applied and the lithium secondary battery is used.
Discharge capacity (mAh) obtained in the capacity confirmation test / Area of the positive electrode mixture layer in the test battery (cm ² ) = Capacity density (mAh / cm ² ) ... (b)

In the lithium secondary battery, it is preferable that the positive electrode potential at the end-of-charge voltage during normal use is 4.30 V (vs. Li / Li ⁺ ) or more. By increasing the positive electrode potential at the end-of-charge voltage during normal use, the energy density of the lithium secondary battery can be increased. Further, in the positive electrode provided in the lithium secondary battery, a film derived from phosphorus oxoacid is formed on the surface of the positive electrode active material, and it is considered that side reactions at the interface between the positive electrode active material and the non-aqueous electrolyte are suppressed. Be done. Therefore, even if the positive electrode potential at the end-of-charge voltage during normal use is set high, the occurrence of a short circuit due to repeated charging and discharging can be suppressed.

It is preferable that the non-aqueous electrolyte contains lithium bis (fluorosulfonyl) imide. When the lithium secondary battery contains lithium bis (fluorosulfonyl) imide in the non-aqueous electrolyte, it is possible to further suppress the occurrence of a short circuit due to repeated charging and discharging.

The positive electrode active material preferably contains a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure or a spinel type crystal structure, or a polyanion compound containing nickel, cobalt or manganese. By using such a positive electrode active material, the capacity retention rate can be increased.

The positive electrode active material has an α-NaFeO type ₂ crystal structure and has a composition of Li _{1 + α} Me _1-α O ₂ (Me is a transition metal element, 1 <(1 + α) / (1-α) <1.6). It preferably contains a lithium transition metal composite oxide represented by the formula. By using such a positive electrode active material, it is possible to increase the energy density of the lithium secondary battery while suppressing the occurrence of a short circuit due to repeated charging and discharging.

The positive electrode active material has an α-NaFeO type ₂ crystal structure, and Li [Li _x Ni _γ Mn _β Co _(1-x-γ-β) ] O ₂ (0 ≦ x <0.5, 0 <γ). , 0 <β, 0.5 <x + γ + β ≦ 1), preferably containing a lithium transition metal composite oxide represented by the composition formula. By using such a positive electrode active material, it is possible to increase the energy density of the lithium secondary battery while suppressing the occurrence of a short circuit due to repeated charging and discharging.

The positive electrode active material has an α-NaFeO type ₂ crystal structure and is a lithium transition metal composite represented by the composition formula of Li [Li _x Co _(1-x) ] O ₂ (0 ≦ x <0.5). It preferably contains an oxide. By using such a positive electrode active material, it is possible to increase the energy density of the lithium secondary battery while suppressing the occurrence of a short circuit due to repeated charging and discharging.

Hereinafter, the lithium secondary battery according to the embodiment of the present invention and the method for manufacturing the lithium secondary battery will be described in detail. Matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art.

<Lithium secondary battery>
A lithium secondary battery according to an embodiment of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a case containing the electrode body and the non-aqueous electrolyte. The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, or a wound type in which a positive electrode and a negative electrode are laminated via a separator. The non-aqueous electrolyte exists in the positive electrode, the negative electrode and the separator.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode mixture layer arranged directly on the positive electrode base material or via an intermediate layer. The positive electrode mixture layer is formed of a so-called positive electrode mixture containing a positive electrode active material.

In the lithium secondary battery, the peak position of P2p exists at 133 eV or less in the spectrum of the positive electrode mixture by X-ray photoelectron spectroscopy. The peak position of P2p may be 132.9 eV or less, 132.8 eV or less, or 132.7 eV or less. Further, the peak position of P2p may be 131 eV or more, 131.3 eV or more, 131.4 eV or more, or 131.5 eV or more.

The peak of P2p appearing in the above range indicates that the compound present on the surface of the positive electrode mixture contains a phosphorus atom in a specific chemical bond state. Such a compound containing a phosphorus atom is usually present on the surface of a particulate positive electrode active material. Such phosphorus atoms suppress side reactions at the interface between the positive electrode active material and the non-aqueous electrolyte. The positive electrode mixture having a peak of P2p of 133 eV or less can be obtained, for example, by drying a positive electrode mixture paste containing an oxo acid of phosphorus. This phosphorus atom is preferably present on the surface of the positive electrode active material as a compound containing a _PO4 anion. In the spectrum by X-ray photoelectron spectroscopy, the peak of P2p of such a compound appears in the range of 131 eV or more and 133 eV or less.

The positive electrode substrate has conductivity. Whether or not it has "conductivity" is determined with a volume resistivity of ¹⁰⁷ Ω · cm measured in accordance with JIS-H-0505 (1975) as a threshold value. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode base material include foils and thin-film deposition films, and foils are preferable from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085 and A3003 specified in JIS-H-4000 (2014).

The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, further preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the positive electrode base material.

The intermediate layer is a layer arranged between the positive electrode base material and the positive electrode mixture layer. The intermediate layer contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode mixture layer. The composition of the intermediate layer is not particularly limited and includes, for example, a resin binder and conductive particles.

The positive electrode mixture layer contains a positive electrode active material and phosphorus oxoacid at least at the time of manufacturing a lithium secondary battery. The positive electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary.

The positive electrode active material can be arbitrarily selected from known positive electrode active materials. For example, a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure, a lithium transition metal composite oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, sulfur and the like can be mentioned.
Examples of the lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure include Li [Li _x Ni _(1-x) ] O ₂ (0 ≦ x <0.5) and Li [Li _x Ni _γ Co ₍₁ ). -X _-γ) ] O ₂ (0 ≦ x <0.5, 0 <γ <1, 0 <x + γ ≦ 1), Li [Li _x Co _(1-x) ] O ₂ (0 ≦ x <0. 5), Li [Li _x Ni _γ Mn _(1-x-γ) ] O ₂ (0 ≦ x <0.5, 0 <γ <1, 0 <x + γ ≦ 1), Li [Li _x Ni _γ Mn _β Co _(1-x-γ-β) ] O ₂ (0≤x <0.5, 0 <γ, 0 <β, 0.5 <x + γ + β≤1), Li [Li _x Ni _γ Co _β Al ₍₁ ) -X _-γ-β) ] O ₂ (0≤x <0.5, 0 <γ, 0 <β, 0.5 <x + γ + β <1) and the like.
Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ .
Examples of the polyanionic compound include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like.
Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like.
The atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface of these materials may be coated with other materials. In the positive electrode mixture layer, one of these materials may be used alone, or two or more thereof may be mixed and used.
Among these positive electrode active materials, a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure or a spinel type crystal structure, or a polyanionic compound containing nickel, cobalt or manganese is preferable from the viewpoint of capacity retention. From the viewpoint of achieving both capacity and capacity retention rate, it is more preferable to use a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure.

The composition ratio of the lithium transition metal composite oxide in the present specification refers to the composition ratio when the lithium transition metal composite oxide is brought into a completely discharged state by the following method. First, the lithium secondary battery is charged with a current of 0.05 C at a constant current until it reaches the end-of-charge voltage at the time of normal use, and is in a fully charged state. After a 30-minute pause, a constant current discharge is performed with a current of 0.05 C to the lower limit voltage during normal use. Disassemble, take out the positive electrode, assemble a test battery with a metal lithium electrode as the counter electrode, and discharge with a constant current until the positive electrode potential reaches 2.0 V (vs. Li / Li ⁺ ) at a current value of 10 mA per 1 g of the positive electrode mixture. To adjust the positive electrode to a completely discharged state. For the metallic lithium electrode here, pure metallic lithium is used instead of a lithium alloy. Re-disassemble and take out the positive electrode. The non-aqueous electrolyte adhering to the removed positive electrode is thoroughly washed with dimethyl carbonate, dried at room temperature for 24 hours, and then the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is used for measurement. The work from dismantling the non-aqueous electrolyte power storage element to collecting the lithium transition metal composite oxide is performed in an argon atmosphere with a dew point of -60 ° C or lower.

The crystal structure of the lithium transition metal composite oxide is determined by X-ray diffraction measurement using CuKα rays. The X-ray diffraction measurement for the lithium transition metal composite oxide is performed on the lithium transition metal composite oxide that has been completely discharged by the above method. Specifically, the X-ray diffraction measurement is performed by powder X-ray diffraction measurement using an X-diffraction device (“MiniFlex II” manufactured by Rigaku), where the radiation source is CuKα ray, the tube voltage is 30 kV, and the tube current is 15 mA. At this time, the diffracted X-rays pass through a Kβ filter having a thickness of 30 μm and are detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width is 0.02 °, the scan speed is 5 ° / min, the divergent slit width is 0.625 °, the light receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm.

Among the lithium transition metal composite oxides having an α-NaFeO type ₂ crystal structure, it is preferable to use a lithium excess type lithium transition metal composite oxide. The lithium-rich transition metal composite oxide is represented by the composition formula Li _{1 + α} Me _1-α O ₂ . In the above composition formula, Me is a transition metal element, and 1 <(1 + α) / (1-α) <1.6. The transition metal element Me preferably contains one or more elements selected from Mn, Co, and Ni, and more preferably contains Mn. The molar ratio of Mn to the transition metal element Me, Mn / Me, is preferably a value larger than 0.5.
The lithium-rich transition metal composite oxide has a high discharge capacity by reaching a relatively high potential exceeding 4.30 V, particularly a potential of 4.40 V or higher, with respect to the redox potential of the lithium metal at least in the first charge. Has the characteristic of being obtained. By combining such a positive electrode active material with a negative electrode using a lithium metal, a lithium secondary battery having a high energy density can be obtained.

The lithium excess type transition metal composite oxide may contain a small amount of a typical element, and it is particularly preferable that it contains Na. The content of Na in the lithium excess type transition metal composite oxide is preferably 1000 ppm or more and 10000 ppm or less, and more preferably 2000 ppm or more and 9000 ppm or less. When the Na content in the lithium excess type transition metal composite oxide is in the above range, the discharge capacity can be increased.

In the composition formula Li _{1 + α} Me _1-α O ₂ , the value of (1 + α) / (1-α), that is, the molar ratio of Li to the transition metal Me, Li / Me, may be more than 1 and less than 1.6. It is preferably 1.1 or more and less than 1.5. By setting Li / Me in the above range, a lithium secondary battery having a large discharge capacity can be obtained. Further, Li / Me is more preferably 1.15 or more and 1.45 or less, and further preferably 1.2 or more and 1.4 or less. By setting Li / Me in the above range, it is possible to obtain a lithium secondary battery having a large discharge capacity and excellent high rate discharge characteristics.

When the transition metal element Me contains Mn, the molar ratio Mn / Me of Mn to the transition metal element Me may be more than 0 and 1 or less, preferably more than 0.5 and 1 or less, and 0.6 or more and 0.75 or less. Is more preferable. By setting Mn / Me in the above range, the discharge capacity can be increased.

When the transition metal element Me contains Co, the molar ratio Co / Me of Co to the transition metal element Me may be more than 0 and 1 or less, preferably 0.05 or more and 0.40 or less, and 0.10 or more. It is more preferably 0.30 or less.

When the transition metal element Me contains Ni, the molar ratio Ni / Me of Ni to the transition metal element Me may be more than 0 and 1 or less, preferably 0.10 or more and 0.50 or less, and 0.15 or more. It is more preferably 0.40 or less.

Examples of the lithium excess type transition metal composite oxide include Li _1.13 Co _0.11 Ni _0.17 Mn _0.59 O ₂ , Li _1.11 Co _0.11 Ni _0.18 Mn _0.60 O ₂ . , Li _1.15 Co _0.11 Ni _0.17 Mn _0.57 O ₂ , Li _1.17 Co _0.11 Ni _0.56 O ₂ , Li _1.05 Co _0.12 Ni _0.19 Mn _0. Examples thereof include ₆₄ O ₂ , Li _1.07 Co _0.12 Ni _0.18 Mn _0.63 O ₂ , Li _1.09 Co _0.11 Ni _0.18 Mn _0.62 O ₂ .

The lithium excess type transition metal composite oxide before charging and discharging is attributed to the space group P3 ₁₁₂ or R3-m. Of these, the one belonging to the space group P3 ₁ 12 is a superlattice peak (Li [Li _1/3 Mn _2/3 ] O ₂ type) near 2θ = 21 ° in the X-ray diffraction diagram using CuKα rays. The peak seen in monoclinic crystals) is confirmed. However, when charging is performed even once and Li in the crystal is desorbed, the symmetry of the crystal changes, the superlattice peak disappears, and the lithium-rich lithium transition metal composite oxide becomes the space group R3-m. It will be attributed. Here, P3 ₁₁₂ is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and the P3 112 model is adopted when the atomic arrangement in R3-m is ordered. Will be done. It should be noted that "R3-m" should be originally described by adding a bar "-" on "3" of "R3m".

The lithium transition metal composite oxide is attributed to either the hexagonal space group P3 ₁ 12 or R3-m, and has a diffraction peak of 2θ = 18.6 ° ± 1 ° in an X-ray diffraction diagram using CuKα rays. It is preferable that the half-value width is 0.20 ° to 0.27 ° or / and the half-value width of the diffraction peak of 2θ = 44.1 ° ± 1 ° is 0.26 ° to 0.39 °. By doing so, it becomes possible to increase the discharge capacity of the positive electrode active material. The diffraction peak of 2θ = 18.6 ° ± 1 ° is on the (003) plane at the Miller index hkl in the space group P3 ₁ 12 and R3-m, and the diffraction peak of 2θ = 44.1 ° ± 1 ° is The space group P3 ₁₁₂ is indexed on the (114) plane, and the space group R3-m is indexed on the (104) plane.

Further, the lithium excess type lithium transition metal composite oxide has an oxygen position parameter obtained by crystal structure analysis by the Rietveld method based on an X-ray diffraction pattern of 0.262 or less in a fully discharged state and 0.267 in a fully charged state. The above is preferable. This makes it possible to obtain a lithium secondary battery having excellent high rate discharge performance. The oxygen position parameter is the spatial coordinate of Me (transition metal) (0,0,0) for the α-NaFeO type ₂ crystal structure of the lithium transition metal composite oxide belonging to the space group R3-m. The value of z when the spatial coordinates of Li (lithium) are defined as (0, 0, 1/2) and the spatial coordinates of O (oxygen) are defined as (0, 0, z). That is, the oxygen position parameter is a relative index indicating how far the O (oxygen) position is from the Me (transition metal) position.

The positive electrode active material is usually particles (powder). The _D50 of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting D ₅₀ of the positive electrode active material to the above lower limit or higher, the production or handling of the positive electrode active material becomes easy. By setting D ₅₀ of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode mixture is improved. When a complex of a positive electrode active material and another material is used, D ₅₀ of the complex is referred to as D ₅₀ of the positive electrode active material. "D ₅₀ " is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by laser diffraction / scattering method for a diluted solution obtained by diluting particles with a solvent. It means a value in which the volume-based integrated distribution calculated in accordance with 2 (2001) is 50%.

A crusher, a classifier, etc. are used to obtain powder with a predetermined particle size. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

The lower limit of the content of the positive electrode active material in the positive electrode mixture is preferably 50% by mass, more preferably 70% by mass, still more preferably 80% by mass. By setting the content of the positive electrode active material to the above lower limit or higher, the energy density of the positive electrode mixture can be increased. On the other hand, the upper limit of the content of the positive electrode active material in the positive electrode mixture may be 100% by mass, 99% by mass or less, or 98% by mass or less. The content of the positive electrode active material in the positive electrode mixture is preferably in the range of not less than any of the above lower limits and not more than any of the upper limits.

The lower limit of the volume density per unit area of the positive electrode mixture layer is preferably 3 mAh / cm ² , more preferably 4 mAh / cm ² , and even more preferably 5 mAh / cm ² . By setting the capacitance density to the above lower limit or higher, the energy density of the lithium secondary battery can be increased. Further, in the conventional positive electrode having such a high capacity density, a short circuit is likely to occur because the current density in the discharge is increased, and the advantages of the present invention can be fully enjoyed. On the other hand, the upper limit of the volume density per unit area of the positive electrode mixture layer is, for example, 20 mAh / cm ² , may be 15 mAh / cm ² , or may be 10 mAh / cm ² . The volume density of the positive electrode mixture layer is preferably in the range of one of the above lower limit or more and one of the upper limit or less.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such a conductive agent include carbonaceous materials, metals, conductive ceramics and the like. Examples of the carbonaceous material include graphitized carbon, non-graphitized carbon, graphene-based carbon and the like. Examples of the non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerenes. Examples of the shape of the conductive agent include powder and fibrous. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Further, these materials may be combined and used. For example, a material in which carbon black and CNT are combined may be used. Among these, carbon black is preferable from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferable.

The content of the conductive agent in the positive electrode mixture layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the lithium secondary battery can be increased.

As the binder, a binder that can fix the positive electrode active material and is electrochemically stable within the range of use is usually used. A water-based binder may be used as the binder, but it is preferable to use a non-water-based binder.

A water-based binder is a binder that is dispersed or dissolved in water. Above all, a binder that dissolves 1 part by mass or more with respect to 100 parts by mass of water at 20 ° C. is preferable as the water-based binder. Examples of the aqueous binder include polyethylene oxide (polyethylene glycol), polypropylene oxide (polypropylene glycol), polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), and polyethylene (PE). ), Polypropylene (PP), nitrile-butadiene rubber, cellulose, etc. Among these, polyacrylic acid, styrene-butadiene rubber (SBR), and cellulose can be used alone or in combination from the viewpoint of coating stability and adhesion. preferable.

The non-aqueous binder is a binder that is dispersed or dissolved in an organic solvent. Above all, a binder that dissolves 1 part by mass or more with respect to 100 parts by mass of N-methyl-2-pyrodrin (NMP) at 20 ° C. is preferable as a non-aqueous binder. Examples of the non-aqueous binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride and hexafluoropropylene copolymer (PVDF-HFP), ethylene and vinyl alcohol copolymer, polyacrylonitrile, polyphosphazene, and poly. Siloxane, polyvinylidene acetate, polyvinylidene methacrylate (PMMA), polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymer of cellulose and chitosanpyrrolidone carboxylate, chitin or chitosan derivative are preferable, among these. From the viewpoint of coating stability and adhesion, polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene (PVDF-HFP), polyimide, and polyamideimide are preferable. Examples of the chitosan derivative include a polymer compound obtained by glycerylizing chitosan and a crosslinked body of chitosan.

Among the above materials, it is preferable to use a fluororesin such as PTFE or PVDF as the binder from the viewpoint of heat resistance, chemical stability, etc., and it is more preferable to use PVDF. As the binder, one type may be used alone, or two or more types may be mixed and used.

The binder content in the positive electrode mixture layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the binder content within the above range, the active substance can be stably retained.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated by methylation or the like in advance.

The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, inorganic oxides such as aluminosilicate, magnesium hydroxide, calcium hydroxide, and hydroxide. Hydroxides such as aluminum, carbonates such as calcium carbonate, sparingly soluble ion crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, etc. Examples include mineral resource-derived substances such as apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, and mica, or man-made products thereof.

The positive electrode mixture layer includes typical non-metal elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba and the like. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as positive electrode active materials, conductive agents, binders, thickeners, fillers. It may be contained as a component other than.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode active material layer containing at least a lithium metal or a lithium alloy as an active material in a charged state.

The negative electrode base material is a conductive material other than lithium metal and lithium alloy. The negative electrode base material is preferably a material that does not react with lithium because lithium metal is deposited. That is, it is preferable that the material does not form an alloy or compound with the lithium metal. Examples of the negative electrode base material include metals such as copper, nickel, stainless steel, and nickel-plated steel, metal materials composed of alloys thereof, and carbon materials composed of activated carbon, graphite, graphene, carbon nanotubes, carbon fibers, and the like. Can be mentioned. Among these, copper or a copper alloy is preferably used because of its high conductivity. The shape of the negative electrode base material is not particularly limited, and may be a foil, a mesh, a porous film, or the like.

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, further preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material in the above range, it is possible to increase the energy density per volume of the lithium secondary battery while increasing the strength of the negative electrode base material.

The lithium secondary battery has a negative electrode active material layer containing a lithium metal or a lithium alloy as an active material at least in a charged state. Examples of the lithium alloy include a lithium alloy containing one or more elements selected from Al, Mg, Ag, In, Sn, Ga, Bi, Pt, and Au. The negative electrode included in the lithium secondary battery may have at least a lithium metal or a lithium alloy in a charged state, and may not have a lithium metal or a lithium alloy in a discharged state. For example, by depositing lithium metal on at least a part of the surface of the negative electrode during charging, the negative electrode has lithium metal in the charged state, and the lithium metal on the surface of the negative electrode is substantially contained in the non-aqueous electrolyte during discharging. The negative electrode may be a lithium secondary battery configured so as to have substantially no lithium metal in the discharged state by eluting all of them as lithium ions.

(Separator)
The separator can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one surface or both surfaces of the base material layer can be used. Examples of the base material layer of the separator include woven fabrics, non-woven fabrics, and porous resin films. Among these, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte.
As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. As the base material layer of the separator, a material in which these resins are combined may be used. The base material layer of the separator may be a complex obtained by adding inorganic particles or the like to these resins.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500 ° C. in an air atmosphere of 1 atm, and are heated from room temperature to 800 ° C. in an air atmosphere of 1 atm. It is more preferable that the mass reduction is 5% or less. Examples of the material whose mass reduction is equal to or less than a predetermined value include inorganic compounds. Examples of the inorganic compound include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide and aluminosilicate; magnesium hydroxide, calcium hydroxide and water. Hydroxides such as aluminum oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride, barium fluoride and barium titanate Covalently bonded crystals such as silicon and diamond; talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, mica and other mineral resource-derived substances or man-made products thereof. .. As the inorganic compound, a simple substance or a complex of these substances may be used alone, or two or more kinds thereof may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the power storage device.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value and means a measured value with a mercury porosity meter.

As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyalkyl methacrylates such as polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyethylene carbonate, polypropylene carbonate, polyvinyl carbonate, and polymethyl methacrylate, polyvinyl ethylene carbonate, polyvinyl acetate, polyvinyl pyrrolidone, polymaleic acid and derivatives thereof. , Polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene and the like. These polymers may be copolymers or mixtures. Further, these polymers may be combined with an inorganic salt or an ionic liquid. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, the above-mentioned porous resin film, non-woven fabric, or the like may be used in combination with the polymer gel.

(Non-water electrolyte)
As the non-aqueous electrolyte, a known non-aqueous electrolyte can be appropriately selected. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitriles and the like. As the non-aqueous solvent, those in which some or all of the hydrogen atoms contained in these compounds are substituted with halogen may be used.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, 1 , 2-Diphenylvinylene carbonate, 4-fluoroethylene carbonate (FEC), 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate (including DFEC, trans, cis and mixtures thereof), trifluoropropylene Carbonate (4- (trifluoromethyl) ethylene carbonate), 4-fluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4- (fluoromethyl) ethylene carbonate, 4,4-bis (fluoromethyl) ) Ethylene carbonate and the like can be mentioned. Among these, 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate and 4,5-difluoroethylene carbonate are preferable, and 4-fluoroethylene carbonate is more preferable, from the viewpoint of increasing the capacity retention rate of the lithium secondary battery.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylphenyl carbonate, ethylphenyl carbonate, diphenyl carbonate, and 2,2,2-trifluoroethylmethyl carbonate (TFEMC). , Ethyl-2,2,2-trifluoroethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethylmethyl carbonate, ethyl-2,2-difluoroethyl) carbonate, bis ( 2,2-Difluoroethyl) carbonate and the like.

As the non-aqueous solvent, it is preferable to use cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. By using the cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte solution can be improved. By using the chain carbonate, the viscosity of the non-aqueous electrolytic solution can be kept low. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

The non-aqueous solvent preferably contains a fluorinated solvent. The fluorinated solvent is a non-aqueous solvent in which a part or all of hydrogen atoms are replaced with fluorine atoms. The content of the fluorinated solvent in the non-aqueous solvent is preferably 20% by volume or more, more preferably 30% by volume or more, further preferably 50% by volume or more, still more preferably 70% by volume or more. The content of the fluorinated solvent in the non-aqueous solvent may be 100% by volume or less. By using such a non-aqueous solvent, it is possible to increase the capacity retention rate when charging and discharging are repeated.

Examples of the fluorinated solvent include fluorinated carbonates, fluorinated ethers, fluorinated esters and the like. Among these, fluorinated carbonate and fluorinated ether are preferable, and fluorinated carbonate is more preferable, from the viewpoint of increasing the capacity retention rate.

Examples of the electrolyte salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO). ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ , etc. Examples thereof include lithium salts having. Among these, an inorganic lithium salt is preferable, LiN (SO ₂ F) ₂ and LiPF ₆ are more preferable, and LiN (SO ₂ F) ₂ is further preferable.

The content of the electrolyte salt in the non-aqueous electrolyte solution is preferably 0.1 mol / dm ³ or more and 2.5 mol / dm ³ or less at 20 ° C. and 1 atm, and 0.3 mol / dm ³ or more and 2.0 mol / dm. It is more preferably ³ or less, more preferably 0.5 mol / dm ³ or more and 1.7 mol / dm ³ or less, and particularly preferably 0.7 mol / dm ³ or more and 1.5 mol / dm ³ or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte solution can be increased.

The non-aqueous electrolyte solution may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additive include halogenated carbonate esters such as 4-fluoroethylene carbonate (FEC) and 4,5-difluoroethylene carbonate (DFEC); lithium bis (oxalate) borate (LiBOB) and lithium difluorooxalate borate (LiFOB). ), Sulfonic acid esters such as lithium bis (oxalate) difluorophosphate (LiFOP); imide salts such as lithium bis (fluorosulfonyl) imide (LiFSI); biphenyl, alkyl biphenyl, terphenyl, partially hydride of terphenyl, cyclohexyl Aromatic compounds such as benzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2, Halogenated anisole compounds such as 4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride. , Maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sulton, propensulton, butane sulton, methyl methanesulfonate, busulphan, toluene sulfonic acid. Methyl, Dimethyl Sulfate, Ethylene Sulfate, Sulfonate, Dimethyl Sulfonate, Diethyl Sulfonate, Dimethyl Sulfoxide, Diethyl Sulfoxide, Tetramethylene Sulfoxide, Diphenyl Sulfate, 4,4'-Bis (2,2-Dioxo-1,3,2-Dioxathiolane) , 4-Methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisol, diphenyldisulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanium , Lithium monofluorophosphate, lithium difluorophosphate and the like. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolytic solution is preferably 0.01% by mass or more and 10% by mass or less, and is 0.1% by mass or more and 7% by mass or less with respect to the total mass of the non-aqueous electrolytic solution. It is more preferable to have it, more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less. By setting the content of the additive in the above range, it is possible to improve the capacity maintenance performance or the cycle performance after high temperature storage, and further improve the safety.

A solid electrolyte may be used as the non-aqueous electrolyte. Further, the non-aqueous electrolyte solution and the solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material having lithium ion conductivity and being solid at 25 ° C. under 1 atm. Examples of the solid electrolyte include a sulfide solid electrolyte, an oxide solid electrolyte, an oxynitride solid electrolyte, a polymer solid electrolyte and the like. Among these, a sulfide solid electrolyte and an oxide solid electrolyte are preferable, and a sulfide solid electrolyte is more preferable because of the high ionic conductivity.

In the lithium secondary battery, the positive potential at the end of charging voltage during normal use is preferably 4.30 V (vs. Li / Li ⁺ ) or more, preferably 4.40 V (vs. Li / Li ⁺ ) or more, or In some cases, it is more preferably 4.50 V (vs. Li / Li ⁺ ) or higher. By setting the positive electrode potential at the end-of-charge voltage during normal use to the above lower limit or higher, the discharge capacity can be increased and the energy density can be increased.
The upper limit of the positive electrode potential at the end-of-charge voltage of the non-aqueous electrolyte power storage element during normal use is, for example, 5.00V (vs. Li / Li ⁺ ) and 4.80V (vs. Li / Li ⁺ ). It may be 4.70 V (vs. Li / Li ⁺ ) or 4.60 V (vs. Li / Li ⁺ ).

The shape of the lithium secondary battery is not particularly limited, and examples thereof include a cylindrical battery, a square battery, a flat battery, a coin battery, and a button battery.
FIG. 1 shows a lithium secondary battery 1 as an example of a square battery. The figure is a perspective view of the inside of the case. The electrode body 2 having the positive electrode and the negative electrode wound around the separator is housed in the square case 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

The lithium secondary battery may be a power source for automobiles such as an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage. It can be mounted as a power storage unit (battery module) composed of a plurality of lithium secondary batteries 1 assembled together. In this case, the technique of the present invention may be applied to at least one lithium secondary battery included in the power storage device.
FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected lithium secondary batteries 1 are assembled is further assembled. Even if the power storage device 30 includes a bus bar (not shown) for electrically connecting two or more lithium secondary batteries 1, a bus bar (not shown) for electrically connecting two or more power storage units 20 and the like. good. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) for monitoring the state of one or more lithium secondary batteries 1.

<Manufacturing method of lithium secondary battery>
The method for producing a lithium secondary battery according to the present embodiment includes producing a positive electrode mixture paste containing a positive electrode active material and phosphorus oxoacid, and drying the positive electrode mixture paste. The lithium secondary battery according to the present embodiment is manufactured by, for example, the following manufacturing method.

(Manufacturing of positive electrode)
The positive electrode can be produced, for example, by applying the positive electrode mixture paste directly to the positive electrode base material or via an intermediate layer and drying the mixture to form a positive electrode mixture layer. The positive electrode mixture paste has a solid content and a dispersion medium. The solid content contains a positive electrode active material and phosphorus oxoacid, and if necessary, contains optional components such as a conductive agent, a binder, a thickener, and a filler. The positive electrode mixture paste can be prepared, for example, by stirring and kneading the positive electrode active material, phosphorus oxoacid, binder, and a conductive agent together with an appropriate amount of a dispersion medium. The volume density per unit area of the positive electrode mixture layer depends on the content of the positive electrode active material in the positive electrode mixture layer, the type of the positive electrode active material, the thickness of the positive electrode mixture layer (the amount of the positive electrode mixture paste applied), and the like. Can be adjusted.

The phosphorus oxoacid refers to a compound having a structure in which a hydroxyl group (-OH) and an oxy group (= O) are bonded to a phosphorus atom. Examples of phosphorus oxo acids include phosphoric acid (H ₃ PO ₄ ), phosphonic acid (H ₃ PO ₃ ), phosphinic acid (H ₃ PO ₂ ), pyrophosphoric acid (H ₄ P ₂ O ₇ ), polyphosphoric acid and the like. Be done. Among these, phosphoric acid and phosphonic acid are preferable, and phosphonic acid is more preferable. By drying the positive electrode mixture paste containing phosphorus oxoacid, a film containing phosphorus atoms can be formed on the surface of the positive electrode active material. In the spectrum by X-ray photoelectron spectroscopy, the peak of P2p of the phosphorus atom derived from the oxo acid of this phosphorus is observed below 133 eV.

The content ratio of phosphorus oxo acid in the positive electrode mixture paste is preferably 0.05 parts by mass or more and 5 parts by mass or less, and 0.07 parts by mass or more and 3 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. It may be 0.08 part by mass or more and 1 part by mass or less, or 0.1 part by mass or more and 0.3 part by mass or less. By setting the content ratio of phosphorus oxoacid in the above range, a film containing a sufficient phosphorus atom for the positive electrode active material can be formed.

Examples of the organic solvent used as the dispersion medium of the positive electrode mixture paste include polar solvents such as N-methyl-2-pyrodrin (NMP), acetone and ethanol, and non-polar solvents such as xylene, toluene and cyclohexane. can. Among these, polar solvents are preferable, and NMP is more preferable.

The method for applying the positive electrode mixture paste is not particularly limited, and can be applied by a known method such as roller coating, screen coating, or spin coating.

(Manufacturing of negative electrode)
A negative electrode is manufactured by forming a layer of lithium metal or a lithium alloy as an active material on the negative electrode base material. The method for forming the layer of the lithium metal or the lithium alloy is not particularly limited, and the method can be performed by a known method such as crimping, electrodeposition, vapor deposition, or sputtering of the lithium metal foil or the lithium alloy foil. The negative electrode included in the lithium secondary battery may have at least a lithium metal or a lithium alloy in a charged state, and may not have a lithium metal or a lithium alloy in a discharged state. For example, by depositing lithium metal on at least a part of the surface of the negative electrode during charging, the negative electrode has lithium metal in the charged state, and the lithium metal on the surface of the negative electrode is substantially contained in the non-aqueous electrolyte during discharging. The negative electrode may be a lithium secondary battery configured so as to have substantially no lithium metal in the discharged state by eluting all of them as lithium ions. That is, in the formation of the electrode body of the lithium secondary battery, the negative electrode may have only the negative electrode base material.

(Preparation of non-aqueous electrolyte)
Prepare a non-aqueous electrolyte. As the non-aqueous electrolyte, for example, a non-aqueous solvent and an electrolyte salt may be mixed and adjusted, or industrially produced and sold ones may be used.

(Assembly of lithium secondary battery)
An electrode body is formed by laminating or winding a positive electrode and a negative electrode via a separator. Next, the electrode body and the non-aqueous electrolyte are housed in the case. The inclusion of the non-aqueous electrolyte in the case can be appropriately selected from known methods. For example, when a non-aqueous electrolyte is used as the non-aqueous electrolyte, the non-aqueous electrolyte may be injected from the injection port formed in the case, and then the injection port may be sealed.

<Other embodiments>
The lithium secondary battery of the present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

[Example 1]
(Preparation of positive electrode)
As the positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure and represented by Li _{1 + α} Me _1-α O ₂ (Me is a transition metal element) was used (hereinafter, “active material”). Also referred to as "A"). Here, the molar ratio of Li and Me, Li / Me, was 1.33, and Me was composed of Ni and Mn, and was contained in a molar ratio of Ni: Mn = 1: 2.
It contains active material A as a positive electrode active material, phosphonic acid as an oxo acid of phosphorus, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder, and contains N-methyl-2-pyrodrin (NMP). ) Was used as a dispersion medium to prepare a positive electrode mixture paste. The ratio of the positive electrode active material, the oxo acid of phosphorus, the conductive agent, and the binder was 93.5: 0.5: 4.5: 1.5 (in terms of solid content) in terms of mass ratio. The adjusted positive electrode mixture paste was applied to one side of an aluminum foil as a positive electrode base material and dried to obtain a positive electrode. The positive electrode was designed and manufactured so that the current density at 1 C was 3.0 mA / cm ² .

(Manufacturing of negative electrode)
A lithium metal foil (100% by mass of lithium metal) as a negative electrode active material was laminated on one side of a copper foil as a negative electrode base material and then pressed to obtain a negative electrode.

(Adjustment of non-aqueous electrolyte)
A mixed solvent was prepared by mixing FEC (4-fluoroethylene carbonate) and TFEMC (2,2,2-trifluoroethylmethyl carbonate) at a ratio of 3: 7. LiPF ₆ as an electrolyte salt was dissolved in this mixed solvent at a concentration of 1.0 mol / dm ³ to prepare a non-aqueous electrolyte.

(Manufacturing of lithium secondary battery)
A microporous polyolefin membrane was used as the separator. An electrode body was produced by laminating the positive electrode and the negative electrode via this separator. This electrode body was housed in a case made of a metal resin composite film, a non-aqueous electrolyte was injected into the case, and the electrode body was sealed by heat welding to obtain a lithium secondary battery of Example 1.

[Comparative Example 1]
A positive electrode mixture paste containing active material A as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder, and using N-methyl-2-pyrodrin (NMP) as a dispersion medium. Was adjusted. The ratio of the positive electrode active material, the conductive agent, and the binder was 94: 4.5: 1.5 (in terms of solid content) in terms of mass ratio. A lithium secondary battery of Comparative Example 1 was obtained in the same manner as in Example 1 except that the positive electrode mixture paste was obtained by the above procedure.

[Reference Example 1]
A negative electrode mixture paste containing graphite as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, and using water as a dispersion medium was prepared. The ratio of the negative electrode active material, the binder, and the thickener was 96.7: 2.1: 1.2 (in terms of solid content) in terms of mass ratio. The adjusted negative electrode mixture paste was applied to one side of a copper foil as a negative electrode base material and dried to obtain a negative electrode.
A lithium secondary battery of Reference Example 1 was obtained in the same manner as in Example 1 except that the negative electrode produced by the above procedure was used.

[Reference Example 2]
A lithium secondary battery of Reference Example 2 was obtained in the same manner as in Comparative Example 1 except that the same negative electrode as in Reference Example 1 was used.

[Example 2]
A lithium secondary battery of Example 2 was obtained in the same manner as in Example 1 except that LiFSI was used instead of LiPF ₆ when adjusting the non-aqueous electrolyte.

[Comparative Example 2]
A lithium secondary battery of Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that LiFSI was used instead of LiPF ₆ when adjusting the non-aqueous electrolyte.

[Comparative Example 3]
A lithium secondary battery of Comparative Example 3 was obtained in the same manner as in Comparative Example 1 except that 1% by mass of phosphonic acid was further added when preparing the non-aqueous electrolyte.

[Example 3]

As the positive electrode active material, a lithium transition metal composite oxide represented by LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used (hereinafter, also referred to as “active material B”).
It contains active material B as a positive electrode active material, phosphonic acid as an oxo acid of phosphorus, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder, and contains N-methyl-2-pyrodrin (NMP). ) Was used as a dispersion medium to prepare a positive electrode mixture paste. The ratio of the positive electrode active material, the oxo acid of phosphorus, the conductive agent, and the binder was 92: 0.5: 4.5: 3.0 (in terms of solid content) in terms of mass ratio. The adjusted positive electrode mixture paste was applied to one side of an aluminum foil as a positive electrode base material and dried to obtain a positive electrode. The positive electrode was designed and manufactured so that the current density at 1C was 6.0 mA / cm ² .
A lithium secondary battery of Example 3 was obtained in the same manner as in Example 1 except that the positive electrode produced by the above procedure was used.

[Comparative Example 4]
A positive electrode mixture paste containing active material B as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder, and using N-methyl-2-pyrodrin (NMP) as a dispersion medium. Was adjusted. The ratio of the positive electrode active material, the conductive agent, and the binder was 92.5: 4.5: 3.0 (in terms of solid content) in terms of mass ratio. A lithium secondary battery of Comparative Example 4 was obtained in the same manner as in Example 3 except that the positive electrode mixture paste was obtained by the above procedure.

[Example 4]
As the positive electrode active material, a lithium transition metal composite oxide represented by LiCoO ₂ was used (hereinafter, also referred to as “active material C”).
It contains active material C as a positive electrode active material, phosphonic acid as an oxo acid of phosphorus, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder, and contains N-methyl-2-pyrodrin (NMP). ) Was used as a dispersion medium to prepare a positive electrode mixture paste. The ratio of the positive electrode active material, the phosphorus oxoacid, the conductive agent, and the binder was 92.50: 0.50: 4.0: 3.0 (in terms of solid content) in terms of mass ratio. The adjusted positive electrode mixture paste was applied to one side of an aluminum foil as a positive electrode base material and dried to obtain a positive electrode. The positive electrode was designed and manufactured so that the current density at 1C was 6.0 mA / cm ² .
A lithium secondary battery of Example 4 was obtained in the same manner as in Example 1 except that the positive electrode produced by the above procedure was used.

[Example 5]
Examples except that the ratio of the positive electrode active material, the oxo acid of phosphorus, the conductive agent, and the binder was 92.75: 0.25: 4.0: 3.0 (solid content equivalent) in terms of mass ratio. In the same manner as in No. 4, the lithium secondary battery of Example 5 was obtained.

[Example 6]
Examples except that the ratio of the positive electrode active material, the oxo acid of phosphorus, the conductive agent, and the binder was 92.90: 0.10: 4.0: 3.0 (solid content equivalent) in terms of mass ratio. In the same manner as in No. 4, the lithium secondary battery of Example 6 was obtained.

[Comparative Example 5]
A positive electrode mixture paste containing active material C as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder, and using N-methyl-2-pyrodrin (NMP) as a dispersion medium. Was adjusted. The ratio of the positive electrode active material, the conductive agent, and the binder was 93.0: 4.0: 3.0 (in terms of solid content) in terms of mass ratio. A lithium secondary battery of Comparative Example 5 was obtained in the same manner as in Example 4 except that the positive electrode mixture paste was obtained by the above procedure.

[Example 7]
The ratio of the positive electrode active material, phosphorus oxo acid, conductive agent, and binder was set to 92.25: 0.25: 4.5: 3.0 (solid content conversion) in terms of mass ratio, and at 1C. A lithium secondary battery of Example 7 was obtained in the same manner as in Example 1 except that the current density was designed to be 6.0 mA / cm ² .

[Comparative Example 6]
The ratio of the positive electrode active material, the conductive agent, and the binder was set to 92.50: 4.5: 3.0 (solid content conversion) in terms of mass ratio, and the current density at 1C was 6.0 mA / cm ² . A lithium secondary battery of Comparative Example 6 was obtained in the same manner as in Example 1 except that the battery was designed to be the same.

[evaluation]
The lithium secondary batteries of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were evaluated under the following conditions.

(Initialization)
In a constant temperature bath at 25 ° C, constant current charge up to 4.60V with a charging current of 0.6mAcm ^-2 , and then constant voltage charging with a constant voltage of ^4.60V until the charging current reaches 0.12mAcm-2. After that, constant current discharge was performed up to 2.00 V with a discharge current of 0.6 mAcm ^-2 . There was a 10 minute rest period between charging and discharging.

(Charge / discharge cycle test)
The lithium secondary battery after initialization is charged with a constant current of 1.2 mAcm ^-2 to 4.60 V in a constant temperature bath at 25 ° C, and the charging current is 0.12 mA cm with a constant voltage of 4.60 V. After constant voltage charging until it became ^-2 , constant current discharge was performed up to 2.00V with a discharge current of 0.6mAcm ^-2 . A 10-minute rest period was provided after each of charging and discharging. These charging and discharging steps were set as one cycle, and this charging / discharging cycle was repeated until a short circuit occurred. The presence or absence of a short circuit was confirmed by a decrease in Coulomb efficiency and an increase in the amount of charging electricity during the charge / discharge cycle. For Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3, charge / discharge cycle tests were performed with three lithium secondary batteries, respectively, and the average number of charge / discharge cycles leading to a short circuit was calculated. , The number of cycles until the short circuit of each Example and Comparative Example was taken. Further, in Example 1 and Comparative Example 3, the discharge capacity in the second cycle was divided by the mass of the positive electrode active material to obtain the initial discharge capacity. Further, for Example 1 and Comparative Example 3, the case volume before initialization and the case volume after charging / discharging in the second cycle were measured, and the amount of increase in cell volume was calculated.

The lithium secondary batteries of Reference Example 1 and Reference Example 2 were evaluated under the following conditions.

(Initialization)
In a constant temperature bath at 25 ° C, constant current charge up to 4.60V with a charging current of 0.1CmA, then constant voltage charging at a constant voltage of 4.60V until the charging current reaches 0.05CmA, and then discharge. A constant current discharge was performed up to 2.00 V at a current of 0.1 CmA. There was a 10 minute rest period between charging and discharging.

(Charge / discharge cycle test)
The lithium secondary battery after initialization is charged at a constant current of 1.0 CmA to 4.60 V in a constant temperature bath at 45 ° C., and the charging current becomes 0.05 CmA at a constant voltage of 4.60 V. After constant voltage charging up to, constant current discharge was performed up to 2.00 V at a discharge current of 1.0 CmA. A 10-minute rest period was provided after each of charging and discharging. The charging and discharging steps were set as one cycle, and this charging / discharging cycle was repeated for 300 cycles. Despite repeated charging and discharging for 300 cycles, no short circuit was observed in the lithium secondary batteries of Reference Example 1 and Reference Example 2.

The lithium secondary batteries of Example 3 and Comparative Example 4 were evaluated under the following conditions.

(Initialization)
In a constant temperature bath at 25 ° C, constant current charge up to 4.40V with a charging current of 0.1CmA, then constant voltage charging with a constant voltage of 4.40V until the charging current reaches 0.05CmA, and then discharge. A constant current discharge was performed up to 2.50 V at a current of 0.1 CmA. There was a 10 minute rest period between charging and discharging.

(Charge / discharge cycle test)
The lithium secondary battery after initialization is charged at a constant current of 0.2 CmA to 4.40 V in a constant temperature bath at 25 ° C, and the charging current becomes 0.05 CmA at a constant voltage of 4.40 V. After constant voltage charging up to, constant current discharge was performed up to 2.50 V at a discharge current of 0.1 CmA. A 10-minute rest period was provided after each of charging and discharging. These charging and discharging steps were set as one cycle, and this charging / discharging cycle was repeated until a short circuit occurred. The presence or absence of a short circuit was confirmed by a decrease in Coulomb efficiency and an increase in the amount of charging electricity during the charge / discharge cycle. A charge / discharge cycle test was performed on each of Example 3 and Comparative Example 4 with three lithium secondary batteries, and the average number of charge / discharge cycles leading to a short circuit was calculated as the number of cycles leading to a short circuit in each Example and Comparative Example. And said.

The lithium secondary batteries of Example 4, Example 5, Example 6, Example 7, Comparative Example 5, and Comparative Example 6 were evaluated under the following conditions.

(Initialization)
In Example 4, Example 5, Example 6, and Comparative Example 5, constant current charging up to 4.55 V with a charging current of 0.1 CmA in a constant temperature bath at 25 ° C., and further charging with a constant voltage of 4.55 V. After constant voltage charging until the current became 0.05 CmA, constant current discharge was performed up to 2.70 V at a discharge current of 0.1 CmA. There was a 10-minute rest period between charging and discharging.
For Example 7 and Comparative Example 6, constant current charging up to 4.6 V with a charging current of 0.1 CmA in a constant temperature bath at 25 ° C., and until the charging current reaches 0.05 CmA at a constant voltage of 4.6 V. After constant voltage charging, constant current discharge was performed up to 2.0 V at a discharge current of 0.1 CmA. There was a 10 minute rest period between charging and discharging.

(Charge / discharge cycle test)
The lithium secondary batteries after initialization in Example 4, Example 5, Example 6, and Comparative Example 5 were constantly charged to 4.55 V at a charging current of 0.2 CmA in a constant temperature bath at 25 ° C. Further, constant voltage charging was performed at a constant voltage of 4.55 V until the charging current became 0.05 CmA, and then constant current discharge was performed at a discharge current of 0.1 CmA to 2.70 V. A 10-minute rest period was provided after each of charging and discharging. These charging and discharging steps were set as one cycle, and this charging / discharging cycle was repeated until a short circuit occurred. The presence or absence of a short circuit was confirmed by a decrease in Coulomb efficiency and an increase in the amount of charging electricity during the charge / discharge cycle.
The lithium secondary batteries after initialization in Example 7 and Comparative Example 6 are constantly charged to 4.6 V with a charging current of 0.33 CmA in a constant temperature bath at 25 ° C., and further charged with a constant current of 4.6 V. After constant voltage charging until the charging current became 0.1 CmA, constant current discharge was performed up to 2.0 V at a discharge current of 0.33 CmA. A 10-minute rest period was provided after each of charging and discharging. These charging and discharging steps were set as one cycle, and this charging / discharging cycle was repeated until a short circuit occurred. The presence or absence of a short circuit was confirmed by a decrease in Coulomb efficiency and an increase in the amount of charging electricity during the charge / discharge cycle.
A charge / discharge cycle test was performed on each of Example 4, Example 5, Example 6, Example 7, Comparative Example 5, and Comparative Example 6 with three lithium secondary batteries, and a charge / discharge cycle leading to a short circuit was performed. The average of the numbers was taken as the number of cycles until the short circuit of each Example and Comparative Example. Further, the percentage of the discharge capacity at the 80th cycle to the discharge capacity at the 2nd cycle was obtained, and the discharge capacity retention rate at the time of the 80th cycle was used. Further, for Example 4, Example 5, Example 6, and Comparative Example 5, the percentage of the discharge capacity at the 150th cycle to the discharge capacity at the second cycle was obtained and used as the discharge capacity retention rate at the time of 150 cycles.

(XPS measurement)
The lithium secondary batteries of Example 1, Comparative Example 1, Comparative Example 3, Example 4, Example 5, Example 6, and Comparative Example 5 after initialization are discharged to 2.00 V at 0.1 CmA. , Completely discharged. Next, the lithium secondary battery was disassembled, the positive electrode was taken out, the positive electrode was thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The positive electrode after drying was cut out and used as a sample for XPS measurement. The work from disassembling the lithium secondary battery to preparing the sample in the XPS measurement was performed in an argon atmosphere with a dew point of −60 ° C. or lower. XPS measurement was performed with the above-mentioned equipment and measurement conditions, and the peak position of P2p in the spectrum of each sample by XPS was confirmed.

The evaluation results are shown in Table 1, Table 2, Table 3, Table 4, and Table 5.

As shown in Table 1, in Example 1 and Comparative Example 1, a short circuit occurred by repeating the charge / discharge cycle. On the other hand, in Reference Example 1 and Reference Example 2, a short circuit did not occur even if the charge / discharge cycle was repeated. It can be seen that the short circuit caused by repeating the charge / discharge cycle is a problem peculiar to the lithium secondary battery that utilizes the precipitation reaction and the elution reaction of the lithium metal as the charge / discharge reaction.

As shown in Table 2, it was confirmed that the lithium secondary battery of the example has a larger number of cycles leading to a short circuit than the lithium secondary battery of the comparative example, and can suppress the occurrence of a short circuit. It was also confirmed that the non-aqueous electrolyte containing LiFSI as an electrolyte salt enhances the effect of suppressing the occurrence of a short circuit.

As shown in Table 2, it was confirmed that Example 1 has a larger number of cycles leading to a short circuit than Comparative Example 3 and can suppress the occurrence of a short circuit. Further, as shown in Table 3, it was confirmed that the cell volume increase in Example 1 was smaller than that in Comparative Example 3, and the volume increase of the lithium secondary battery could be suppressed. Further, it was confirmed that Example 1 can have a larger initial discharge capacity as compared with Comparative Example 3.

As shown in Table 4, it was confirmed that the lithium secondary battery of the example has a larger number of cycles leading to a short circuit than the lithium secondary battery of the comparative example, and can suppress the occurrence of a short circuit.

As shown in Table 5, it was confirmed that the lithium secondary battery of the example has a larger number of cycles leading to a short circuit than the lithium secondary battery of the comparative example, and can suppress the occurrence of a short circuit. Further, it was confirmed that when the active material C was used as the positive electrode active material, the discharge capacity retention rate was lower than that when the active material A was used. Further, in the lithium secondary battery using the active material C as the positive electrode active material, the content of H ₃ PO ₃ as the oxo acid of phosphorus in the positive electrode mixture paste is 0.3 mass by mass with respect to 100 parts by mass of the positive electrode. It was confirmed that the decrease in the discharge capacity retention rate can be suppressed by reducing the amount to less than one part.

Although the present invention has been described in detail above, the above-described embodiment is merely an example, and the invention disclosed here includes various modifications and modifications of the above-mentioned specific examples.

1 Lithium secondary battery 2 Electrode body 3 Case 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Power storage unit 30 Power storage device

Claims

A method for manufacturing a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte.
The negative electrode contains a lithium metal or a lithium alloy as an active material in a charged state, and contains a lithium metal or a lithium alloy.
To prepare a positive electrode mixture paste containing a positive electrode active material and phosphorus oxoacid,
Drying the positive electrode mixture paste and
A method for manufacturing a lithium secondary battery.
The production of the lithium secondary battery according to claim 1, wherein the content of the phosphorus oxoacid in the positive electrode mixture paste is 0.05 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. Method.
The content of oxoacid of phosphorus in the positive electrode mixture paste is 0.1 part by mass or more and 0.3 part by mass or less with respect to 100 parts by mass of the positive electrode active material.
The lithium according to claim 2, wherein the positive electrode active material contains a lithium transition metal composite oxide represented by the composition formula of Li [Li x Co (1-x) ] O 2 (0 ≦ x <0.5). How to manufacture a secondary battery.
A positive electrode with a positive electrode mixture containing a positive electrode active material, and
A negative electrode containing lithium metal or a lithium alloy as an active material in a charged state,
Equipped with non-aqueous electrolyte,
A lithium secondary battery in which the peak of P2p exists at 133 eV or less in the spectrum of the positive electrode mixture by X-ray photoelectron spectroscopy.
The positive electrode comprises a positive electrode mixture layer containing the positive electrode mixture.
The lithium secondary battery according to claim 4, wherein the capacity density per unit area of the positive electrode mixture layer is 3 mAh / cm 2 or more.
The lithium secondary battery according to claim 4 or 5, wherein the positive electrode potential at the end-of-charge voltage during normal use is 4.30 V (vs. Li / Li + ) or more.
The lithium secondary battery according to any one of claims 4 to 6, wherein the non-aqueous electrolyte contains a lithium bis (fluorosulfonyl) imide.
The present invention according to any one of claims 4 to 7, wherein the positive electrode active material contains a lithium transition metal composite oxide having an α-NaFeO type 2 crystal structure or a spinel type crystal structure, or a polyanion compound containing nickel, cobalt or manganese. The lithium secondary battery described.
The positive electrode active material has an α-NaFeO type 2 crystal structure and has a composition of Li 1 + α Me 1-α O 2 (Me is a transition metal element, 1 <(1 + α) / (1-α) <1.6). The lithium secondary battery according to claim 8, which comprises a lithium transition metal composite oxide represented by the formula.
The positive electrode active material has an α-NaFeO type 2 crystal structure, and Li [Li x Ni γ Mn β Co (1-x-γ-β) ] O 2 (0 ≦ x <0.5, 0 <γ). , 0 <β, 0.5 <x + γ + β ≦ 1) The lithium secondary battery according to claim 8, which contains a lithium transition metal composite oxide represented by the composition formula.
The positive electrode active material has an α-NaFeO type 2 crystal structure and is a lithium transition metal composite represented by the composition formula of Li [Li x Co (1-x) ] O 2 (0 ≦ x <0.5). The lithium secondary battery according to claim 8, which comprises an oxide.